The present invention is directed to a printed document including a print quality indicator and a method of determining the print quality of the printed document.
It is well known that images which are to be printed typically undergo distortion and degradation to a greater or lesser degree during the various steps of the printing process. For example, as an image goes from a photographic negative, where it may be very clear, to a plate, from the plate to a printing blanket, and finally from the blanket onto the document substrate in an offsetlithography printing operation, the quality of the image will necessarily decline to some degree at each stage of the process.
It is common in the printing industry to measure and control the quality of images printed on documents. It is also common to measure and control the quality of the images at each successive stage in the printing process. For example, if the quality of the image on the photographic negative or on the plate is too low, printed documents of less than acceptable quality will necessarily result and there is no need to go to the expense of printing documents using such a negative or plate in order to measure quality. In commercial printing operations, print quality targets of various graphical configurations, sometimes referred to as "control bars," are printed in trim areas of a sheet or web. One difficulty with such control bars is that they are not within the primary printing area of the sheet or web, so that the observed or measured quality of the printing of the control bars on the printed sheet or web may not accurately reflect the quality of the print image within the primary printing area. Another difficulty with such control bars is that since they are printed within trim areas, they are removed with the trim areas during finishing operations and therefore do not permit a quality assessment of the documents to be subsequent to finishing. Another difficulty with such control bars is that there use is limited to documents that include trims areas, and numerous business forms do not include trim areas. Another drawback of prior art printed quality targets of this type is that they are designed to measure primarily mechanical dot gain, i.e. the gain experienced in halftone dot size, of mid-size halftone dots. They do not provide an indication of the sharpness or print quality of the halftone dots.
Other types of self-contained quality control targets have been printed in the primary printing areas of documents--solid density boxes, built into borders of various designs, dot area targets, included within the pantograph screened area of documents, and extremely small alpha-numeric characters, termed microprint characters, also included within the pantograph screened area of documents. None of these arrangements, however, has provided a quantitative means for evaluating dot structure. Characteristics of dot structure include shape, size, and edge definition. Previously, the dots and microprint characters were magnified and visually inspected, and a subjective assessment was then made as to the quality of the printing. Because of the subjective nature of this process, it has not been possible to articulate an objective quality standard for such products.
It is seen therefore that there is a need for a printed document including a print quality indicator and for a method of determining the print quality of the printed document in which the print quality indicator may be printed within the primary printing area of the document and in which an objective, repeatable measure of print quality can be obtained.